Alright, so just gave Reward Flight searching a go.
If you access the "Book A Flight" via the VFF home page (i.e. go to the "Redeem" menu), you'll get the 401 error as shown above. Very odd page they seem to be trying to point to for that frame.
If you go to the VA home page, then log into VFF using the link in the top right, then use the Book A Flight box on the left hand side of the home page, but tick "Use Points+Pay", you will be able to see reward seats and prices etc.
What is odd is that when I get to the fare matrix on the next page, the system doesn't appear to recognise that I am logged into VFF, i.e. I see the two boxes for VFF# and password on the right hand side, whereas if it had recognised my login it should show my name and points balance.
I didn't follow through with a booking to check whether I'd have to log in again, but that's still all weird.
Also, at least once when I was doing lots of dummy inputs on the VA home page for reward seat searches, I'd get a 405 error (Apache return error page). Since this is not a consistent error, I wonder what is going on there.